[3.5] BBEG wants to sit on the mountain and watch the tigers fight

[hymer]

Trivial solution: Disguise self as one of PCs. Appear in tavern, and brag about plan to kill dragon. Do this in different times and places. Done.

Slightly more advanced: Hire the PCs to kill the dragon, preferably through an intermediary who doesn't know your true identity and will honestly believe the offer to hire is genuine. Now the threat to the dragon is real.

More cunning: Manipulate the dragon into approaching you as an oracle. Lie.

Thanks for replying!
As for getting the PCs involved, that won't work. Half of them aren't human, and they have no political power as of yet. They would get killed, but not by an invading army. They're also not important enough, yet, to be on the radar screen of Rothgor or any dragon. They've helped thwart one of Rathgor's servants, so he probably doesn't even know their names.
A fake oracle sounds like an interesting idea. Care to elaborate?

@ facelessminion: Rothgor will need to make plans without relying on PCs or other human adventurers, I'm afraid. Thanks, though.